For production of an alpha-olefin polymer, especially an ethylene homopolymer or an ethylene/alphaolefin copolymer, a method has heretofore been known to polymerize ethylene or copolymerizing ethylene with an alpha-olefin in the presence of a titanium-containing catalyst comprising a titanium compound and an organoaluminum compound or a vanadium-containing catalyst comprising a vanadium compound and an organoaluminum compound.
Catalyst comprising zirconium compounds and aluminoxanes have recently been proposed as a new Zieglertype olefin polymerization catalyst.
Japanese Laid-Open Patent Publication No. 19309/1983 describes a process for polymerizing ethylene and at least one C.sub.3 -C.sub.12 alpha-olefin in the presence of a catalyst composed of a transition metal-containing compound represented by the following formula EQU (cyclopentadienyl).sub.2 MeRHal
in which R is cyclopentadienyl, C.sub.1 -C.sub.6 alkyl, or halogen, Me is a transition metal and Hal is halogen, and a linear aluminoxane represented by the following formula EQU Al.sub.2 OR.sub.4 (Al(R)-O).sub.n
in which R is methyl or ethyl, and n is a number of 4 to 20, or a cyclic aluminoxane represented by the following formula ##STR1## in which R and n are as defined above, at a temperature of -50.degree. C. to 200.degree. C.
Japanese Laid-Open Patent Publication No. 95292/1984 describes an invention relating to a process for producing a linear aluminoxane represented by the following formula ##STR2## in which n is 2 to 40, and R is C.sub.1 -C.sub.6, and a cyclic aluminoxane represented by the following formula ##STR3## in which n and R are as defined. This patent publication discloses a specific example in which methylaluminoxane, for example, produced by the process of this patent publication is mixed with a bis(cyclopentadienyl) compound of titanium or zirconium, and an olefin is polymerized in the presence of the mixture.
Japanese Laid-Open Patent Publication No. 35005/1985 discloses a process for producing an olefin polymerization catalyst, which comprises reacting an aluminoxane represented by the following formula ##STR4## in which R is C.sub.1 -C.sub.10 alkyl, and R.sup.o is R.sup.1 or is bonded to represent --O--, with a magnesium compound, chlorinating the reaction product, and treating the chlorinated product with a compound of Ti, V, Zr or Cr. This patent publication describes that the above catalyst is especially suitable for copolymerization of a mixture of ethylene with a C.sub.3 -C.sub.12 alpha-olefin.
Japanese Laid-Open Patent Publication No. 35006/1985 discloses a combination of (a) a mono-, di- or tri-cyclopentadienyl compound of two or more different transition metals or its derivative and (b) an alumoxane (aluminoxane) as a catalyst system for production of a reactor blended polymer.
Japanese Laid-Open Patent Publication No. 35007/1985 describes a process for polymerizing ethylene alone or together with an alpha-olefin having at least 3 carbon atoms in the presence of a catalyst system comprising a metallocene and a cyclic aluminoxane represented by the following formula ##STR5## in which R is an alkyl group having 1 to 5 carbon atoms, and n is an integer of 1 to about 20, or a linear alumoxane represented by the following formula ##STR6## in which R and n are as defined above.
Japanese Laid-Open Patent Publication No. 35008/1985 discloses that by using a catalyst system containing at least two metallocenes and an alumoxane, polyethylene or an ethylene/C.sub.3 -C.sub.10 alpha-olefin copolymer having a broad molecular weight distribution is produced.
The catalysts formed from transition metal compounds and aluminoxanes as proposed in these prior art references have much higher polymerization activity than catalyst systems formed from transition metal compounds and organoaluminum compounds known heretofore. But these catalyst systems are soluble in the reaction systems, and the resulting polymer has a low bulk density. It is difficult to obtain polymers having excellent powder characteristics.
On the other hand, the above-cited Japanese Laid-Open Patent Publications Nos. 35006/1985, 35007/1985 and 35008/1985 propose methods in which catalysts formed from a solid catalyst component deposited on a porous inorganic oxide carrier such as silica, silica-alumina or alumina and an aluminoxane are used. Japanese Laid-Open Patent Publications Nos. 31404/1986, 108610/1986 and 106808/1985 propose methods in which a solid catalyst component deposited on a similar porous inorganic oxide carrier is used. In many of the methods described in these prior art references, the polymerization activity is reduced, or the resulting polymers have insufficient powder characteristics such as low bulk density as a result of using the deposited solid components.